High resolution nuclear magnetic resonance (NMR) spectroscopy of liquid samples is a widely utilized analytical technique in diverse applications ranging from pharmaceutical discovery and development of new drugs, to on-line reaction monitoring, to human biomarker metabolomics. A market for affordable, high-performance, low maintenance cost, small footprint magnets already exists and should grow significantly in this decade.
A typical all-low temperature superconducting (LTS) NMR magnet wound with NbTi and/or Nb3Sn wires requires operation either at <4.2 mostly with use of liquid helium (LHe). The magnet has three operational challenges: 1) high susceptibility to quench, because of its extremely low thermal stability; 2) large size, because of the low-current carrying capacities of LTS at ≧12 T; and 3) high cryogenic cost, because of its reliance on LHe. Although a zero boil-off cryogenic system is now a Magnetic Resonance Imaging (MRI) market standard and even used in some NMR magnets, helium prices have doubled from 2002 to 2007 and are still rising. A high temperature superconducting (HTS) magnet operated at ≧10 K, may provide practical solutions to these challenges; inherent thermal stability; higher current-carrying capacities; and no absolute requirement for operation at <10K.
HTS magnets may be formed by coils of a superconducting material, for example single- or double-pancake. As shown by FIG. 1, the superconducting material may be in the form of a thin tape 110. The tape 110 may be wrapped or layered with an insulating material. The tape 110 may be wound around a circular bobbin (not shown), to form a first coil 120. Then the second coil 140 may be continuously wound on top of the first coil 120, for example, on the same bobbin, to form a double-pancake (DP) coil structure 200, as shown by FIG. 2, where there is a cross-over turn 125 between the first coil 120 and the second coil 140.
Insulation is generally considered indispensable to both superconducting and resistive electromagnets. However, except for ensuring a specific current path within a winding, insulation is undesirable in several aspects. First, the insulation, generally organic, makes a winding elastically soft and increases mechanical strain of the winding under a given stress (“spongy effect”). Second, insulation reduces the overall current density of the winding. For example, in the case of 2G (second generation) HTS having an overall thickness is nearly the same as that of a typical insulator, the current density may be reduced roughly by half. Third, insulation electrically isolates every turn in a winding and prevents, in the event of a quench, current bypassing through the adjacent turns, which may cause overheating in the quench spot. Therefore, use of thick stabilizer, typically Cu, to protect HTS magnets from permanent damage is common, resulting in large magnets. While recent progress in the current-carrying capacity of 2G HTS makes it feasible to build >35 T superconducting magnets, these issues still remain big technical challenges.
In general, magnet protection, for example, from over-heating in an event of quench, is one of the major factors that limit HTS magnet current density. Therefore, there is a need in the industry to overcome the abovementioned shortcomings.